In the related art, there are image forming apparatuses such as multi function peripherals (hereinafter referred to as “MFPs”) and printers. An image forming apparatus includes a fixing device. The fixing device includes a heating roller and a belt. The belt is suspended on a plurality of rollers. The fixing device forms a nip between the heating roller and the belt. The fixing device fixes a toner image on a recording medium by heat of the heating roller. The fixing device is controlled in a fixing mode and a decolorizing mode. In the fixing mode, a toner image is fixed to a recording medium. In the decolorizing mode, a toner image is decolorized from the recording medium. In the decolorizing mode, the temperature of the heating roller is set to be higher than in the fixing mode. For example, when the fixing mode is switched to the decolorizing mode, the heating roller is heated. Conversely, when the decolorizing mode is switched to the fixing mode, the heating roller performs idle running for natural cooling. However, with only the idle running of the heating roller, it may take an undesirably long time to sufficiently cool the heating roller. Therefore, there is a possibility that a time in which a user may not use the image forming apparatus occurs.